This study examines obese and lean individuals on two standard diets (which differ by calorie content) and the stool and urine energy losses to compare these values in lean versus obese individuals. The study is also investigating the specific macronutrient content of stool to examine differences in these parameters between lean and obese individuals. The repeatability of these measurements is also being tested in a subset of individuals. In collaboration with Dr. Jeffrey Gordons lab at Washington University in St. Louis, samples of stool will be sent for determination of the fecal bacterial flora phylotypes to examine the association between stool energy loss and enteric flora populations. Results of this study are expected in late 2008.